Investments of Insurance Subsidiaries - Schedule of Maturities of Investments (Detail) $ in Millions	Sep. 30, 2020 USD ($)
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 4
Due after one year through five years, Amortized Cost	127
Due after five years through ten years, Amortized Cost	175
Due after ten years, Amortized Cost	78
Amortized Cost, Total	384
Due in one year or less, Fair Value	4
Due after one year through five years, Fair Value	135
Due after five years through ten years, Fair Value	192
Due after ten years, Fair Value	84
Fair Value, Total	$ 415

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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